Testing the methodology for a dosimetric end-to-end audit of IMRT/VMAT: results of IAEA multicentre and national studies

Abstract

Introduction: Within an International Atomic Energy Agency (IAEA) coordinated research project (CRP), a remote end-to-end dosimetric quality audit for intensity modulated radiation therapy (IMRT)/ volumetric arc therapy (VMAT) was developed to verify the radiotherapy chain including imaging, treatment planning and dose delivery. The methodology as well as the results obtained in a multicentre pilot study and national trial runs conducted in close cooperation with dosimetry audit networks (DANs) of IAEA Member States are presented. Material and methods: A solid polystyrene phantom containing a dosimetry insert with an irregular solid water planning target volume (PTV) and organ at risk (OAR) was designed for this audit. The insert can be preloaded with radiochromic film and four thermoluminescent dosimeters (TLDs). For the audit, radiotherapy centres were asked to scan the phantom, contour the structures, create an IMRT/VMAT treatment plan and irradiate the phantom. The dose prescription was to deliver 4 Gy to the PTV in two fractions and to limit the OAR dose to a maximum of 2.8 Gy. The TLD measured doses and film measured dose distributions were compared with the TPS calculations. Results: Sixteen hospitals from 13 countries and 64 hospitals from 6 countries participated in the multicenter pilot study and in the national runs, respectively. The TLD results for the PTV were all within ±5% acceptance limit for the multicentre pilot study, whereas for national runs, 17 participants failed to meet this criterion. All measured doses in the OAR were below the treatment planning constraint. The film analysis identified seven plans in national runs below the 90% passing rate gamma criteria. Conclusion: The results proved that the methodology of the IMRT/VMAT dosimetric end-to-end audit was feasible for its intended purpose, i.e., the phantom design and materials were suitable; the phantom was easy to use and it was robust enough for shipment. Most importantly the audit methodology was capable of identifying suboptimal IMRT/VMAT delivery.

A multi‐institutional evaluation of small field output factor determination following the recommendations of IAEA/AAPM TRS‐483

“…Approximately 67% of the centers participating in the present study were also participating in clinical trials involving stereotactic radiotherapy and/or intensity modulated radiotherapy techniques where accurate dosimetry of small fields is essential. The proposed linac‐type‐curves along with the proposed tolerance limits can be used as initial quality assurance for the accreditation for clinical trials followed my more detailed experimental procedures 4–6 …”

IAEA methodology for on-site end-to-end IMRT/VMAT audits: an international pilot study

“…In addition, there is an advantage of the auditor presence during the on-site measurement session. For example, IROC-Houston utilizes 7% tolerance for point dose measurements with thermoluminescent dosimeters (TLDs) in PTV for IMRT H&N credentialing [34]; the same tolerance is adopted in the national remote IMRT/VMAT audit pilot run using lithium formate dosimeters in Sweden [35]; 5% tolerance is used for alanine point dose measurements in the national IMRT audit using a slab phantom in the UK [36]; and 5% tolerance is also used for the PTV in the IAEA remote audit of IMRT/VMAT head treatments with TLD [13]. Consequently, the tolerance levels of 5% and 7% in PTVs and OAR, respectively, used in the audit methodology here are comparable to those of the existing audit systems using a similar type of audit and phantom.…”

“…The IAEA has developed several auditing methodologies which involve measurements of absorbed dose to water for high-energy photon and electron beams in non-reference conditions including end-to-end audits for 3D conformal and intensity modulated RT treatments [9][10][11][12][13]. Although these audits are not provided directly by the IAEA as a regular service, their methodologies are available for implementation at a national level by a local DAN with the IAEA support [14][15][16][17].…”

Comprehensive end-to-end test for intensity-modulated radiation therapy for nasopharyngeal carcinoma using an anthropomorphic phantom and EBT3 film

“…Therefore, this type of testing is also recommended after treatment planning system commissioning by AAPM TG-40 and after treatment planning system changes by AAPM TG-142, and TG-53 (9)(10)(11) . Most extant studies on the end-to-end test are based on considerably simple phantoms (12)(13)(14)(15)(16) . Recently, anthropomorphic phantoms that realistically simulate anatomically accurate patient tissue heterogeneities were introduced to end-to-end IMRT/VMAT dosimetry audit methodology and monthly QA protocol for external beam radiation therapy treatment (17,18) .…”